With reference to FIGS. 1 and 2, the prior art structure for baseballs and softballs is illustrated. Two covers 10a, 10b close the ball core 40 by using seaming wires 30. Each of the covers 10a, 10b has two large round portions at two ends and the middle portion connected to the two round portions are narrowed. At the edge of each cover 10a, 10b near the seaming portion is installed with a protrusion 20 so that the ball can be controlled preferably.
However, in the manufacturing process, the covers 10a, 10b must be made to have a shape matching the protrusions 20. Then the protrusions 20 must be glued into the lower sides of the covers 10a, 10b manually. Then the covers 10a, 10b are seamed by the seaming wires 30. The process is complicated and great work time is necessary. Moreover, the shape of the protrusion 20 must match the shape of the covers 10a, 10b so that a great part of the material for protrusions are wasted and thus cost is increased.